Trace Evidence: Fiber
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Fibers
• Used in forensic science to create a link between a crime
and a suspect.
• Considered to be CLASS EVIDENCE because they are
mass produced.
• Sensitive evidence – 95% of all fibers may be lost within
24 hours.
• Only the fibers you would not expect to find are
investigated.
– Example: pink fibers found all over the victim’s body found on a
pink carpet vs. pink fibers found on a suspect’s pants
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Sources
• Fibers can originate from many sources:
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Carpet
Clothing
Linen
Furniture
Insulation
Rope/ligature
Tape
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Two Types of Fibers
• Natural
– derived from plants or animal hair
• Synthetic
– manmade
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Natural Fibers: Animal Fibers
• Sheep (wool)
• most common; the end use is often determined by
coarseness
• fine wool fibers are used for clothing, while coarse
wool fibers are used in carpeting
• Goat (mohair, cashmere)
• Camel (wool)
• Llama
• Alpaca (wool)
• Fur fibers from mink, rabbit, beaver, etc.
• Silk (fiber from the cocoon of the silkworm)
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Natural Fibers: Plant Fibers
• Cotton (ribbon-like shape with irregular twists; most common)
• Flax (Linen)
• Ramie
• Sisal (often used in linen rugs)
• Jute (used in ropes)
• Hemp (the common name for cannabis for industrial or nondrug use; typically used for rope or sack)
• Kapok (fiber from kapok tree seed pods; used in pillows and
mattress stuffing)
• Coir (coconut husks; used in carpet, rugs)
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Synthetic Fibers
More than half of all fibers used in the production of textile
materials are manmade.
• Polyester (most common; wrinkle resistant; often spun with
cotton)
• Nylon (very common; elastic and strong; lustrous and silk-like
when stretched)
• Acrylics (wool-like, soft and warm; quick drying and resistant
to moths)
• Rayon (cellulose-derived, regenerated, thin fiber)
• Acetates (cellulosed-based, wrinkle-resistant fiber)
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Special Fibers
• Aramid fiber is a light, but strong, synthetic fiber.
• Heat-resistant aramid fiber is typically used for bulletproof vests, military applications, and racing tires
• Fire-resistant aramid fiber is used for firemen or disaster
response teams.
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Types of Fibers
• Fiber – a fine, slender piece of thread or filament
• Yarn – a twisted aggregate of fibers
• Textiles – woven fibers; fabrics
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Weaving
Lengthwise threads (the warp) are woven by crosswise threads
(the weft) in a pattern.
Common Weave Patterns
• Plain (firm, tends to wrinkle)
• Basket (not very durable, shrinks when washed)
• Satin (not durable, shiny surface)
• Twill (very strong, dense and compact, soft)
• Leno (open weave, easily distorted)
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Fiber Comparisons
• Microscopic Comparisons
• Color
• Diameter
• Surface markings
• Delustering agents
• Cross-sectional shape
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Fiber Comparisons (continued)
• Polarized Light Microscopy – determines birefringence
(difference between two refractive indices) using polarized light
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Fiber Comparisons (continued)
• Fourier Transform Infrared Spectroscopy (FTIR) –
analysis of a fiber’s chemical composition based on its ability
to absorb light at different wavelengths
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Fiber Comparisons (continued)
• UV-Visible Microspectrophotometry – distinguishes
slight/subtle color differences based on absorption of light at
different wavelengths
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Significance of Fiber Evidence
Two Possible Conclusions in Fiber Comparisons
• The Questioned fiber could have originated from the Known
sample.
• The Questioned fiber did not originate from the Known
source.
• The number of fibers is directly proportional to the likelihood of
actual contact (i.e., the greater the number of fibers, the more
likely that contact actually occurred.)
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Significance of Fiber Evidence
(continued)
Greater number of fiber types
More unique the material
Greater significance
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Resources
• Saferstein, Richard. Forensic Science: An Introduction.
New Jersey: Pearson Prentice Hall, 2008.
• Saferstein, Richard. Criminalistics: An Introduction to
Forensic Science. 8th ed. Upper Saddle River, NJ:
Pearson Prentice Hall, 2004.
• Saferstein, Richard. Forensic Science Handbook.
Englewood Cliffs, NJ: Prentice-Hall, 1982.
• Bertino, Anthony J. Forensic Science: Fundamentals and
Investigations. Mason, OH: South-Western Cengage
Learning, 2009.
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